Time comparison system



March 22,1960 c. w. SKELTON TIME COMPARISON SYSTEM 2 Sheets-Sheet 1 Filed April 24, 1957 7 3/ .D T R L 12 w w m m ,3 M L V 9 T L 4 MW a m /.W DL NP I mm 2 O V R 9 0 -W J! E a R THRESHOLD INVENTOR FREQUENCY D/V/DER ORNEYS AMPL/F/ER CLOCK WORKS Charla; W 616655011 BY mfiw, w fm OSCILLATOR PHASE SPLITTER POWER AMPL/F/ER March 22, 1960 Filed April 24, 1957 C. W. SKELTON TIME COMPARISON SYSTEM 2 Sheets-Sheet 2 I I a {3 E E 4 36 1 i i as I.

INVENTOR Claa'les 7158102650121 ATTORNEYS United States Patent TIME COMPARISON SYSTEM Application April 24, 1957, Serial No. 654,951

9 Claims. (Cl. 324-68) This invention relates to an apparatus for comparing a locally produced time indication with a radio transmitted standard with means to correct the locally produced indication until it corresponds with the standard.

A radio time standard is continuously transmitted by sending a time tick or signal once every second. By detecting this signal and using it to drive a clock mechanism or the like, remotely located stations and stations on moving vehicles can keep track of the exact time in accordance with the transmitted standard. However, because of interference and other causes, a station may not be able to receive the time tick over varying intervals lasting several days.

During this time it is necessary for such stations .to rely on locally generated time signals. When the standard signal is again received, it is necessary to correct the locally generated indication to correspond with the standard. The apparatus according to the present invention provides a system for quickly and accurately observing the error between the locally generated indication and the standard and then by a simple turn of the knob, the local indication can be corrected to precisely correspond with the standard. This observation and correction can be easily carried out for errors as small as milliseconds.

Briefly described, the locally generated indication comprises a 60 cycle per second source which is used to drive signal to the band pass an opaque disk at a rate of one revolution per second.

'Ihe opaque disk has defined therein an arrow shaped aperture. The radio time tick is detected and controls the energization once every second of a strobe light which illuminates the arrow shaped aperture. The displacement of the arrow shaped aperture from a norm at the time of illumination gives a precise and easily perceived indication ofv the error between the standard and the local time. A control means is provided to delay or advance .the phase of the 60 cycle signal. By a simple adjustment of this control means, the point of illumination of, the arrow shaped aperture can cide with the norm and when this adjustment is made, the local indication will correspond exactly to the radio standard.

The objects and advantages can be better appreciated from the description with reference to the drawings wherein:

Figure 1 shows a block diagram of the time-tick detecting part of the system.

Figure 2 illustrates an external view of the apparatus showing the indicator and the control dials.

Figure 3 shows a block diagram of the system for generating the local indication.

Figure 4 shows a section through the center of Figure 2.

The standard time signal used in this invention is modulated on a radio frequency which i continuously transmitted. It consists of a thousand cycle pulse of 0.005 second or 5 cycles in length. This pulse is repeated at a rate of once every second. In the intervalsbetween the be made to coinpulses, the radio frequency is modulated with 440 or 600 cycles per second.

Referring now to Figure 1, the system for detecting this time signal is shown. The receiver 10 detects the radio signal and demodulates it and applies the resulting amplifier 11. The demodulated signal applied to the band pass amplifier consists of thousand cycle pulses coming at intervals of once every second while a frequency of 440 or 600 cycles is applied to the band pass amplifier betweenthe pulses. pass amplifier 11 transmits only signals having a frequency between the range of 900 and 1100 cycles per second. The applied to the one shot multivibrator 12. The only signal applied to the multivibrator is the 1000 cycle pulses coming once every second. The one shot multivibrator is actuated to produce a DC. output pulse each time it receives one of these pulses. Along with the 1000 cycle pulses applied to the multivibrator there will also be some noise. Most of this noise will be of insuflicient amplitude to actuate the multivibrator. The amplitude necessary to cause actuation can be varied by means of i 14, which is adjusted so that all amplitude of the 1000 cycle pulses,

the threshold control signals just below the being received from the amplifier 11 will not have enough amplitude to actuate the multivibrator. In this manner, the optimum amount of noise is made ineffective. The one shot multivibrator 12 applies its D.C. output pulses to the strobotron 13. Upon receiving each pulse, the strobotron is energized and produces a brief illumination. Hence, the strobotron 13 will give off a brief pulse of light once every second at the same time that the receiver 10 detects the 1000 cycle time tick.

Figure 3 shows a block diagram of the system for o produce an output frequency of 122.88 kilocycles per second. The oscillator employs a GT cutgenerating flie local indication of time. An oscillator is designed to crystal so that this frequency is very accurately maintained. The frequency output of the oscillator is fed to a frequency divider 21 which divides the input frequency by two to the eleventh power. The frequency divider therefore produces an output of 60 cycles per second. This output is produces at its output a three phase supply of 60 cycles per second. The output from the phase splitter is fed to an amplifier 20 and the amplifier applies the signal to the stator windings 24 of a self-synchronous repeater, each phase being applied to a separate one of the three windings. A single phase 60 cycle signal is picked up by the rotor winding 25 of the synchronous repeater and is applied to the power amplifier 26. This 60 cycle signal induced in the rotor winding is the local indication of time. After amplification, this signal is applied to and drives the clock works 27.

Referring now to Figure 4, the clock works 27 is used to drive a shaft 28 at a reduced rpm. The shaft 28 drives a gear 29. The gear 29 engages with the gear 30 mounted on the ring 33. The ring 33 is mounted in the bearing 32, which is supported by the casing 37. Inside the ring 33 is mounted a reflector 35 and supported within the reflector 35 is the strobotron 13 which produces a light pulse once every second as was explained in the description with reference to Figure l. The reflector covering 35 directs the light pulses to illuminate one side of an opaque disk 31 which is fixed to the ring 33 so that it covers one end thereof. The gear 29 drives the gear 30 so that the opaque disk 31 makes one revolution per second as controlled by the locally generated 60 cycle signal. is a translucent screen 36 casing 37.

The band' amplified output from the amplifier 11 is fed to a phase splitter 22 which Covering the opaque disk 31] which is mounted on the h standard time indication.

. dex'ing point.

The front view of the apparatus can be seen in Figure 25 An arrow shaped aperture 34 is defined in the disk 31. This aperture permits the passage of light to the translucent screen causing an. arrow. shaped. image .to appear on the screen at the position of the .aperture each time. the -st10b0t1011 is energized. Around the edges of is, divided into 100 equal divisions.

The indexing mark at thetop, of the ring-is designated by the numeral .0. Every 1,0 marks goingto the left and to the right are designated v100, 200, etc., down to the in? dexing mark at thebottomofthe .r-iug designated 500.

These designation numerals on the. indexing ring representv the diflerence betweenthe lo'calindication and the standard'timetickin milliseconds, each division on the in-. dexing'ring being milliseconds. The indexing mark atwhich the. arrow image appears will represent. the

error between the two time signals,

' In operation, the disk 31'will be makingone revolution persecond and the strobotronlii whichis mounted,be-. hind theopaque disk 31 will illuminate thearrow. aper-.

ture 34, once every second. The diskfil is driven by the 60"cyclelocal time'indication while the illumination. of the; arrowshaped aperture is controlled by the radio will appearatthe same position which is arbitrarily set at the zer'o'mark. However, when the local, indication comprising the6O cycle signal begins to difier from the standard-"radio received" time indlcation, the point. of illuminaticn 'of the, arrow willmove'ioffthe zeromark to-theright or to the left, depending upon whether. the.

local indication-is aheadof orbehindthe standard. The

aniountot deviation of. the illuminated. aperture willcor-respondtothe amount of error between the two, signals'. If the local indication is. one tenth-.ofla second ahead of the radiostandardthen the arrow shaped image will appear one tenth of the way around the indeXing ring since the disk is making one revolution per second.

The point of "illumination then will, beatthe indexing mark designated 100 indicating an error 'of 100 millithe-phase of the signal induced on the rotor until this" signal corresponds with the-radio standard: This change the. rotating diskiil. isfla fixed indexing ring- 38 which" As long as these two time. indications are in synchronism, the arrow shapedaperture arsen l I in phase of the signal will of course effecttherotation of thedisk 31 and the rotor 25 need merely be rotated until'thearrow' image again (coincides with the zero in- One revolution of the rotor 25willadvance or-retard-the phase ofthe-signal one whole cycle of5*the-60 cycle signal'which will be one sixtiethof' asecondi This amounts to about 17 mill-isecondsi( actually 16 /3 milliseconds)so that to advance or retard the arrow: 34 17' milliseconds the'rotor 25 will have tomake 'ap-' proximately one complete revolution. The rotor 25 is rotated by turning the knob 39 -mounted on the' right side of the disk and'indexingring" 38; encircled by an indexing ring-40 which 'isdivided into seventeenths, each division representing a correctionof' approximately one millisecond.

The knob 15 mounted orrthe left side offthe:di'sk-:3'1

controls the threshold. 1.4; which was described. with:

reference to Figure 1. H 7

As long-as the maximum error between theadjustments;

ofjhe local signal is less :than a half a second, the error between the standard frequency and thelocally generated. 60;.cycle signal canbe quickly and easily ascertained: If;

the maximumerrorbetweenthe two signals is over half asecond, then..this.,system. will rbe inadequate since the operator 'willnot know whether the device is delayed or The knob is advanced behind the signal. norm... However, by using a temperature stabilized GT cut crystal oscillator, .the.

. and that nurnerous'modifications -may be made therein Without departing from the spirit and scope of the inventioniias set forthJin the appended claims.

What is claimed is:

1. Means for comparing a first time signal with the standard radio time-tick comprising a rotatable indicating member, means to rotate said member in synchronism with said first time signal only, and means to illuminate at least part of said member with pulses of light in synchronism with said standard radio time tick.

2. A time comparison device asrecited-in claim-l wherein said indicating. member comprises a disk1hav-- ingran aperture'definednear. the edge thereof andfsaidj illuminating'means illuminates one side of saiddiskl so as toshine'through said aperture.

3. A time comparison device as. recited in claim 2 wherein there is provided'al-st'ationary ring having index-.. ing markings thereon surroundingsaid disk.

41 A" time comparison device as recited in claim. 1: wherein'means is provided 'to indicate the displacementoif said memberfrorna normeach time it is illuminatedby one of said pulses of light.

5. A timing system comprising means to generate a.-

multi-phase alternating current supply, a self synchronous repeater havinga plurality of stator windings and a roton. winding; circuit means for applying a separate phase or] said alternating current supply to eachof said stator windings, a timing. mechanism for keeping track ofrtime in responseto an applied frequenW, and circnitrneans! to apply. the signal induced in said rotor windir'ig tojsaid. timing mechanism.

6. An apparatus for maintaining synchronism between;

a first time system and a standard time system comprising means to generate a multiphase alternating CHIIIlt'Sig-j nal, a self-synchronous repeater having a plurality off stator windings and a rotor winding, circuit means for applying a separate phase ofsaid alternating currentfsignal to each of said statorwindings, a rotatable indicat-" iug member, means to rotate said member in synchronism'.

with the signal-induced on-said rotor winding, and means toilluminate at least part'of said member with pulses of light at a timerate'in-synchronism withsaid standard time system. 7

7. Means for comparing'a first time signal with the:

standard radio time'tick comprising a rotatable indicating member, means to rotate said member in synchronism" with said first time signal only means to illuminate'ar leastpart of said'member with pulses oflight in synchrm nism with said standardradiotime tick thereby topresent" a visual-indication of-the relationship between said first" .time signal'and'said radio. time tick, andjmearisfdf variably changing-the visually indicated relationshipbe tween said first time signal and said radio time tick;

8. A"timing system comprising means to generate a multi phase alternating current supply,- a self-synchronous repeater having a plurality of stator windings and a'roto'r" apply the signalinduced in said' rotor winding to said timing mechanism, and means for variably adjusting tlie phase relationship between one or" said stator windings and said.rotor winding, 7

9. An apparatus for maintaining synchronism between a first time system and a,s tandard.time system compris ing meansutovgenerateamultiphase alternating currenu;

sig 1 ,1a l,,a. self-s nchr n us repe t r hairingia P HFEI-ityJQfiL.

stator windings and a rotor winding, jeircuit means for relationship between one of said stator windings and said applying a separate phase of said alternating current sigrotor winding.

nal to each of said stator windings, a rotatable indicating References Cited in the file of this patent member, means to rotate said member in synchronism with the signal induced on said rotor winding, means 5 UNITED STATES PATENTS to illuminate at least part of said member with pulses 1,936,683 Morrison Nov. 28, 1933 of light at a time rate in synchronism with said standard 2,114,714 Kalsey Apr. 19, 1938 time system, and means for variably adjusting the phase 2,724,969 Bloser Nov. 29, 1955 

